The present invention relates a watercraft having a closed loop coolant circulating system with at least one heat exchanger constituting an exterior surface of the hull.
Many small, recreational watercraft, such as personal watercraft (PWC), are powered by water-cooled two-stroke internal combustion engines. These engines use open-loop cooling systems that draw water through a water intake from the body of water through which the watercraft is traveling, circulate that water through the water jacket of the engine to absorb heat from the engine and then expel the water through an outlet back to the environment. Typically, the water inlet for such an open-loop system is located between the impeller and the venturi of the watercraft propulsion system so that a small volume of pressurized water is diverted to the engine water jacket and then to the outlet without the need for a dedicated water pump.
This open-loop cooling system performs adequately for many types of engines, including many two-stroke engines, which are not especially sensitive to temperature for optimal operating conditions. Nevertheless, an open-loop cooling system has certain drawbacks.
First, with an open-loop system, debris or contaminants from the environment (such as leaves, aquatic plants, mud and even small insects and marine animals) can enter the open system, thereby partially or completely obstructing passage(s) and/or reducing the efficiency of the cooling system.
Second, when operating the watercraft in salt water, the cooling system""s pipes and water jacket manifold become susceptible to corrosion due to the presence of salt within the water flowing through the cooling system. To prevent such corrosion from occurring, it is necessary to use corrosive-resistant materials and/or surface treatments on the cooling system components. This increases the cost of the components and complicates design and manufacture. Further, even when using such materials or coated components, it is advisable to flush the seawater from the system after use to minimize its damaging effects. This is also time-consuming and inconvenient.
Furthermore, with an open-loop system the temperature of the ambient water introduced into the system from the environment can change considerably, depending on the season and/or location, by as much as 40xc2x0 F. or more. This makes it more difficult to regulate the desired cooling effect of the system and keep the engine in the desired operating temperature range.
U.S. Pat. No. 5,507,673 to Boggia (the ""673 patent) discloses a watercraft having an internal combustion engine and a closed coolant circulating system. Because the coolant circulating system is closed, the problems discussed above with respect to open-loop cooling systems are obviated. However, the coolant circulating systems of the ""673 patent does not provide sufficient heat exchanging surface to properly dissipate engine heat from the coolant because the coolant is passed only through the tubular members that constitute the grate covering the impeller tunnel intake opening. The theory behind this construction is that the coolant inside the grating tubular members will dissipate heat from the coolant therein to the water flowing through the grate into the impeller tunnel. However, in practice this is an impractical construction because the grate""s tubular members fail to provide a sufficient amount of surface area to allow the coolant therein to effectively dissipate heat.
Consequently, there exists a need in the art for a watercraft with an improved closed coolant circulating system that provides sufficient heat exchanging surface area to allow heat from the engine to be dissipated to ambient water in an effective manner without the drawbacks associated with the system.
To meet the above-described need, the present invention provides a watercraft for travelling along a surface of a body of water comprising a hull having an exterior surface; an engine constructed and arranged to generate power, the engine also generating heat during the generation of power; and a propulsion system operatively connected to the engine and being constructed and arranged to propel the watercraft along the surface of the body of water using the power generated by the engine. The watercraft of the present invention further comprises a closed coolant circulating system containing a supply of coolant that is caused to flow through a fluid path during operation of the engine. The circulating system has an engine heat absorbing portion through which the coolant flows. The engine heat absorbing portion is positioned with respect to the engine such that at least a portion of the heat generated by the engine is absorbed by the heat absorbing portion and the coolant flowing therethrough.
A heat exchanger is formed from a heat conductive material and has a heat exchanging fluid path defined therein with an inlet port and an outlet port. The heat exchanger has a heat exchanging exterior surface and is mounted to the hull such that the heat exchanging exterior surface constitutes a portion of the exterior surface of the hull that is normally disposed below the surface of the body of water when the watercraft is in an upright position. The inlet and outlet ports are respectively communicated to the engine heat absorbing portion such that the heat exchanging fluid path constitutes a portion of the coolant circulating system with the coolant flowing into the heat exchanging fluid path from the heat absorbing portion via the inlet port and from the fluid path back to the heat absorbing portion via the outlet port. The heat conductive material of the heat exchanger allows the heat absorbed from the engine by the coolant to dissipate from the coolant to the body of water via the heat exchanging exterior surface as the coolant flows through the fluid path.
With such a closed coolant circulating system, there is no opportunity for debris or contaminants from the environment to enter the system and blocking passages, thereby reducing the efficiency of the closed coolant circulating system.
In addition, because the coolant circulating system is closed, water from the body of water on which the watercraft is travelling is not allowed to enter the cooling system. Therefore, it is not necessary to take the special steps discussed above to prevent corrosion from occurring within the coolant circulating system due to the watercraft""s use in salt water. Nor does the coolant circulating system need to be flushed when the watercraft is operated in salt water.
A particularly advantageous feature of the present invention is that the heat exchanger is mounted to the hull such that the heat exchanging exterior surface thereof constitutes a portion of the exterior surface of the hull that is normally disposed below the surface of the body of water when the watercraft is in an upright position. As a result of this construction, the heat exchanger can be provided with a relatively large heat exchanging exterior surface, which contacts the body of water. Also, because the heat exchanging surface constitutes a portion of the hull""s exterior surface, the heat exchanger takes advantage of a large amount of available surface area in the watercraft that already exists to provide the heat exchanging surface. Consequently, heat exchanging can be achieved in a more effective and efficient manner than in the construction disclosed in the ""673 patent discussed above.
In one preferred aspect of the invention, the engine is a four-stroke internal combustion engine. The introduction of more stringent emissions standards has led watercraft designers to look for four-stroke engines that run cleaner than two-stroke engines. In a two-stroke engine, lubricating oil is usually either mixed with the fuel or injected into the intake tract for lubricating the pistons, rings, cylinder walls, bearings, etc. This oil entering the combustion chamber results in a greater amount of incompletely combusted hydrocarbons in the exhaust of the typical two-stroke engine. On the other hand, in a four-stroke engine, oil is not mixed with fuel to lubricate the walls of the cylinders. Instead, oil is routed through passages in the piston and connecting rod assembly for lubricating the sides of the piston head. Therefore, less oil reaches the combustion chamber and hydrocarbon emissions are reduced.
The operation of many four-stroke engines is, however, more sensitive to temperature and requires a reliable cooling system capable of maintaining the engine operating temperature within an optimal, narrow range. An open-loop cooling system that simply circulates water from the body of water through which the watercraft travels is inadequate for such temperature-sensitive four-stroke engines because, as discussed above, the temperature of the water drawn into the open loop cooling system can vary greatly due to environmental conditions. By using the closed-loop coolant circulating system of the present invention in combination with a four-stroke engine, the problems associated with variations in ambient water conditions can be minimized.
In another preferred aspect of the present invention, the heat exchanger has a plate-like configuration and is a ride plate mounted at an underside stem portion of the hull along a centerline thereof. In this aspect, the heat exchanger and the ride plate define an impeller tunnel having a rearward discharge opening at the stem and a forward intake opening spaced forwardly of the discharge opening. The propulsion system includes an impeller assembly mounted to the ride plate/heat exchanger within the tunnel. The impeller assembly has an impeller with a plurality of blades, which is connected to the engine so as to rotate under power from the engine such that the impeller draws water out from the tunnel through the discharge port is a pressurized stream to propel the watercraft.
This preferred aspect is particularly advantageous because it takes advantage of an existing structure, the ride plate, which is normally made from heat conductive material. Specifically, the ride plate of a watercraft is typically made from metal so that it is rugged enough to withstand impacts with submerged objects during high speed operation of the watercraft. Modifying the ride plate so that it also functions as a heat exchanger advantageously allows the present invention to be implemented without modifying the hull itself so as to incorporate the heat exchanger on the exterior of the hull itself.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.